In application Ser. No. 683,662 filed May 6, 1976, and assigned to the same assignee as this application, an assembly is disclosed for internal circumferential welding of abutting hollow tank sections or courses.
The apparatus includes three longitudinally spaced, axially aligned, rotatable rings. The center ring includes a plurality of circumferentially spaced, radially directed jacks each extendible the same distance regardless of the resistance encountered by a particular jack to force the abutting edges of the tank sections into a precise circular cross section and support and hold the abutting edges in aligned relation during rotation and welding. The other two rings include circumferentially spaced radially directed jacks of the seek-and-find type that will automatically extend until all jacks exert the same force on the tank sections extending from each side of the center ring to thereby support the tank sections for rotation about the common axis of the three rings, regardless of whether the tank sections are of cylindrical, right frusto-conical or scalene frusto-conical shape.
A longitudinal conveyor extends within the rings to move tank courses to be welded longitudinally into end-to-end abutting contact in the center ring. However, the longitudinal conveyor has not always been effective to bring the courses into abutting contact throughout the circumferential joint. This is particularly true if one course is out of round relative to the adjacent course, or if one course is slightly misaligned relative to the other course and gaps occur about the periphery of the abutting joint. While the center jacks tend to reduce the gaps and obtain a circular abutting joint for welding, slight longitudinal misalignment can cause considerable operator time to be spent attempting to achieve longitudinal alignment and abutting contact of the courses along the periphery of the joint to be welded, before a satisfactory abutting joint can be obtained for welding. Thus the production rate of the apparatus is reduced and the welding assembly line can be held up while the courses are aligned in the center ring and a satisfactory joint for welding is obtained.